Radar video recording system

ABSTRACT

A radar data system for recording and replaying radar information for energizing a search radar display unit and having a capability of accommodating a plurality of search radars of either the two-dimensional or three dimensional type. In addition, provision has been made to allow for the variety of signals used to define the search radar position and also for internal fault detection. Also, the system can record and provide command and control signals for external simulators and/or computer systems to perform a wide variety of functions which may be related to the recorded search radar presentations. The system is divided into two primary sections, record and reproduce, and is further subdivided according to the type of data being recorded on a recorder track.

8 e. Unite States Patent [191 11 Buchholz et al. 1 Apr. 3, 1973 [54] RADAR VIDEO RECORDING SYSTEM 3,662,388 5 1972 Mott et a]. .343 5 Pc x [75] Inventors: Donald E. Buchholz, Silver Spring;

i Ronald L. Bakala, Laurel; Robert E. 5 Exammer '.r' Tubbesmg ttorney-R. S. Sctascra, J. A. Cooke and R. J. Miller, Elhcott; Richard W. Plcker- Erickson ing, Burtonsville, all of Md. [73] Assignee: The United States of America as ABSTRACT represented by the Secretary of the A radar data system for recording and replaying radar Navy information for energizing a search radar display unit 22 i May 17, 1971 and having a capability of accommodating a plurality of search radars of either the two-dimensional or three [21] APPL 144,103 dimensional type. In addition, provision has been made to allow for the variety of signals used to define 52 us. Cl .3435 PC, 35/104 the Search radar P-* and also for internal fault 51 Int. Cl G015 7/02 the f ecmd and Pmvide [58] Field of Search ..343 5 R 5 PC' 35/10 4 mand and slgnals enema Simulatms I and/or computer systems to perform a wide variety of functions which ma be related to the recorded search [56] References Cited radar presentations? The system is divided into two UNITED STATES PATENTS primary sections, record and reproduce, and is further subdivided according to the type of data being Tsumura et ai recorded on a recorder track 3,588,896 6/1971 Duarte ..343/ PC 3,634,887 1/1972 Buchholz et al. ..343/5 PC Claims, 15 Drawing Figures n: L1 g I IO i i VIDEO 5 5 CONDITIONER s w o I 1 l M ID I I TRK g a I 2 a g I i O l TRK CONVERTER o g l FROM VIDEO 4 1 I E summers 4 2mm: J 2 i i I GE :A rR svucimo 2 E I PROGRAM l z I CONTROL 29 E a w I 22 ANALOG SOALAR 2 l9 I iu m CONVERTER m i AID I l m 2 g 20 CONVERTER I g t 1 23 DIGITAL Ix {Y g g g I 2| /24 I l GONVER'I'ER IPULSE I 26 [TRAINS n: 1 couvenrsn l I 27 28 on FOR- TRK comm 3| GATE MATTER 3 neconen rme a ID i T rm: TIME i 8 ID 27 I v I DISPLAY I l I l l INHIBIT i l l I ssu=-resr I i i I l DISPLAY l PAIENIEDIPR: I973 SHEET OEUF 13 RANGE RADlUS.\// BEARING I J l I [fix I v I /l/b l I/ ANTENNA I 5 1,3); BEARING Fl 6. 2 I .1 I KX/ANTENNA HORIZON ELEVATION DATA VIDEO FL 1's '|"W|I'- -I|"HII'IIIWII- M,

TE TM 7 TM BLANKING PERIOD FIG. 4

PATENTEDAPR3 ms 3, 5,912

SHEET USUF 13 BEAR ING so w sm o.aee(+) 1 cos o.5oo(-) FIG.6

PATENTEUAPRB 1975 3 5,912

' SHEET DSUF 13 \MASTER CONTROLLER GATE I I I A85 [I77 I I EVEN l I GATE SHIFT I FROM REGISTER I FIG-Jo I83 1 I R E 12) F e 10 I i E 8 GATE I v 1 V 000 I80 I89 1 I90 5 I GATE 7 I88 1 r/ I78 FORMAT I I CONVERTER V ODD I GATE SHIFT I REGISTER B'POLAR 4 1 1 DRIVER GATE T0 FIG. 7c l9l a w FIG 70' {:EQORDEZ] RADAR VIDEO RECORDING SYSTEM BRIEF SUMMARY OF THE INVENTION This invention relates to a system that can record signals from one, two, or three search radars simultaneously. The radars may be either two or three dimensional systems. More specifically, the subject invention records real-time radar signals for subsequent reproduction into a radar display system. Antenna bearing and elevation angle signals are also processed in addition to the output of the radar receivers. The subject invention is divided into a video channel and a data channel. The video channel receives video signals, such as targets and clutter, along with various reference triggers and an elevation angle signal. The video is modulated, the triggers are conditioned, and the elevation angle is converted into a simple binary pulse train. All of these signals are summed and recorded on a magnetic tape. A separate track of a magnetic recorder is assigned for the video of each radar being recorded. The data channel receives the bearing information and various auxiliary inputs, such as coded-time signals. The data coming into this channel may be in either analog or digital form. The data channel converts all input data into a common digital format, places the data into a serial address system, and stores the data from all radars on a single track of the magnetic recorder. In the reproduce mode the subject invention can either deliver all signals in their original format to a display system or take those radar signals that were originally analog signals and reproduce them in a digital format. Of course, the converse can be performed, i.e. radar signals that were originally in a digital format can be received and reproduced as analog data, thereby permitting the recording of realistic presentations of aircraft raids that can be played back into the same weapons system or other weapons systems.

It is therefore an object of the invention to provide a digital recording system that will permit acquisitions of live radar environmental situations.

Another object of the invention is to provide a digital radar system that will collect data for analyzing special radar environments. I

Another object of this invention is to provide a system which accommodates up to three search radars of two-dimensional and/or three-dimensionalcapabili- Still another object of the invention is to provide a digital recording system whose reproductions are indistinguishable from the original radar video displays.

It is another object of the invention to produce a flexible and reliable system that will reproduce radar display information without degradation of initial signal qualities.

A further object of the invention is to provide a digital recording system that can be advantageously used for personnel training and for radar system evaluation. A v

Another object of the invention is to provide a digital recording system which permits collection ofradar data for real-time analysis.

A still further object of the invention is to provide a digital system which can record and reproduce command' and control signals for external simulators and/or computer systems to perform -a wide variety of functions which may be related to the recorded search radar presentations.

Still another object is to provide a digital recording system which may be used in developing specialized radar video processing equipment for a simulating radar and weapons system.

It is another object of the invention to provide a system which is capable of processing other analog and/or digital data for recording and playback.

And still another object of the invention is to provide a digital system which provides a capability of recording and playback for an EW (electronic warfare) simulator, the control signals of which system may be used to generate an EW environment corresponding to the search radar presentation.

Other objects, features, and characteristics of the invention will become more apparent and discernible when reference is made to the detailed description and also to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 6 is a chart showing the quadrant locations of 7 bearing angles;

FIGS. through 7d are companion parts of a detail block diagram of the record portion of the data channel of the subject invention; and

FIGS. 8a through 8d are companion parts of a detailed block diagram of the reproduce portion of the data channel of the subject invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention consists broadly of two functional systems, i.e., a video channel and a data channel. For eachof these systems there is a section relating to the record mode and a section relating to the reproduce (playback) mode. Referring to FIG. 1, it will be observed that the subject invention comprises a video record channel 2, a video reproduce channel 3, a data record channel 4, and a data reproduce channel 5.

The video system consists of three channels, which are practically identical. Each channel of the video function uses a separate tape track on a magnetic recorder 6. The data channel 4 uses a single channel and a single tape track. Thus the system can be thought of as having four functional channels, i.e., three video and one data.

The video record channel circuitry 2 prepares the video and associated information for the magnetic recorder 6. The video channels receive from each radar video signals 7, trigger signals 8 and elevation angle signals 9. The video signals 7 are modulated in a conditioner 10, which may conveniently comprise a pulse peak detector or a pulse width detector. The trigger signals 8 are shaped in a conditioner 11, which may be similar to the conditioner 10, and the elevation signals 9 are converted into a binary pulse train by a converter 12. The video record channel 2 combines all these signals into a single composite video signal 13. In the video reproduce channel 3, the circuitry essentially separates the various signals from the composite video signals 13 via detectors 14, restores them to their original parameters via conditioners 15 and I6 and converter 17, and feeds them out as independent signals.

The data record channel 4 receives radar bearing signals 18 from independent sources. The radar bearing signals 18 come in all forms: scalar analog signals 19, synchro analog signals 20 or digital pulse trains 21. Regardless of the type of incoming radar bearing signals, they are converted into the proper digital signal by either of digital converters 22 or 23. The selected digitized radar bearing signal is gated in an OR gate 24 with timing signals 31. The gating sequence is determined by a program control unit 25. The data record channel 4 then formats all signals via a formatter 26 into a single multiplexed digital signal 27.

Like the video reproduce channel 3, the data reproduce channel 5 separates all the information contained in the multiplexed digital signal 27 via a decoder 28, reproduces it via an analog converter 29 and a digital converter 30 and feeds it out to display systems or other equipment. Because all signals were originally converted to a common digital signal, a unique feature of the system is available. For instance, suppose that sine and cosine values came into the system as synchro analog signals and that these were coded into a digital format and then recorded. It is possible with the subject invention to retrieve these data in their digital form and, in the reproduce circuitry, output them as either synchro analogs or digital pulse trains. Thus one type of radar display system may be used when recording signals, and a different type of radar display system may be used to display the signals.

Certain search radars are capable of fixing an aircraft in two dimensions, as is shown in FIG. 2. Because the radar in pointing in a particular direction at the moment that it receives the echo pulse, knowing the bearing angle for that moment places the aircraft in bearing. By measuring the elapsed time from transmit to receive, the radar can also determine the range of the aircraft. This radar, however, cannot fix the aircraft at a specific elevation angle because its antenna shape is such that an echo pulse can come in from many angles in the elevation plane. This type of radar (with bearing and range data) is therefore considered a two-dimensional system. It produces a master trigger, TM, which, as a reference point, indicates when the pulse was transmitted. It also produces a video signal which is the received echo pulse and is delayed from the master trigger by an amount proportional to range.

With reference now to FIG. 3 other types of radars are known as three-dimensional systems because they can fix an aircraft at a specific elevation angle, in addition to hearing and range. They are able to do this by having an antenna array that directs the beam within narrow sectors of the elevation plane. In a sense, then, the antenna scans not only in bearing, but also in elevation. These radars also produce another trigger, a reference point which denotes end of sweep. Since the end-of-sweep trigger, TE (FIG. 4) occurs at the start of a blanking period and just a short time before the master trigger, it is also referred to as the early trigger. During the first portion of elevation scan a surface trigger, TS, is generated for each scan. Each time the radar crosses the horizon (or 0 elevation) it also generates a horizon trigger, Tl-I With reference again to FIG. 1, channel 2 contains circuitry for processing the video signals 7 and all the trigger signals 8 that might come from a three-dimensional radar. Since the threedimensional radar is simultaneously scanning in elevation, it also receives an analog signal 9 representing the elevation angle during that particular scan. This analog is converted into a coded binary number since recording it as it comes in would require a separate tape track just for the analog signal. The binary number takes up only a small portion of the scan time and is therefore easily fitted into the blanking period of the video signal. The triggers are encoded according to polarity, and the video is modulated to provide a signal that most easily fits into the bandpass of the magnetic recorder. The triggers are summed together with the modulated video and coded elevation to produce the composite video signal, as shown in FIG. 4.

With reference now to FIGS. 5a and 5b, there is shown a detailed block diagram of the record and reproduce channels 2 and 3, respectively, of the video system. A master trigger (TM) 33, an end-of-sweep trigger (TE) 34, a horizon trigger (TH) 35, and a surface trigger (TS) 36 are each applied to conditioning circuits 37, 38, 39 and 40, respectively, wherein a logic voltage level is established for each signal. The signals emergent from the conditioning circuits 37 through 40 have a standardized voltage logic level and are then applied to a pulse encoder circuit 41 which is essentially a monostable multivibrator for producing a standardized pulse width. Also within encoder circuit 41, the standardized triggers are coded with difierent polarities for gating into the format used in recording the signals on tape. Early and master trigger signals from the radar system are converted into positive pulses, whereas horizon trigger signals and surface trigger signals are converted into negative pulses.

Video signals for all three video channels are each in the form of a varying, positive DC voltage level. This DC signal cannot be directly recorded by the magnetic recorder. For this reason, video modulator 10 modulates the radar video signal at a specified high frequeni cy rate (e.g. one megahertz) to provide a bipolar signal useable by the magnetic recorder 6.

To produce the composite video that is recorded, the triggers [except for TS (FIG. 4)] and the modulated video signal must be summed and delayed. This is performed in a summing amplifier 32a and a delay circuit 32b. Summing amplifier 32a also inverts the TE TM, and TH pulses. These inversions make the TE and TM pulses in the composite video-signal negative, while the TH signal is positive. The three triggers retain their original timing relationship with respect to the video signal and to each other. The output of the summing amplifier 32a is combined with the negative TS signal in a summing amplifier 42 along with a serialized elevation signal 47a to produce the composite video signal 13 which contains the composite video, the four trigger signals, and the serial elevation data.

Elevation data from three-dimensional radar systems is in the form of an analog signal V, sine E. Video channels l and 2 contain identical circuitry for converting the analog signal into a serial digital signal and inserting sampling; when the signal retums to zero,the sample and hold circuit switches to a hold mode. In this'way the data is sampled at each radar sweep, revising the elevation data that is recorded. A comparator 45, sequencer 46 and storage register 47, along with sample and hold circuit '43, from a closed loop analog-todigital converter 12. In comparator 45 the parallel count 48 from the storage register 47 is converted to an analog signal which is summed 'with the sample and hold analog output 49. This summed signal is compared to a reference voltage to produce an error signal 50 from comparator 45 .The error signal 50 from the com-- parator 45 is either positive or negative as lon'gas'the output count from thestorage register 47 doesnot match the analog input signal 49 to the comparator. The polarity of errorsignal 50 indicates whether bits inserted into storage register 47 make the total count too large or too small. When the analog signal derived from the parallel count 48 is equal to the sample andfhold" amplifier output 49, the error signal SO-is zero and the conversion is complete. Analog-to-digital conversion begins in sequencer 46 by a start signal 51- from the isolation amplifier 44. This start signal occurs at the trailing edge of the TM signal 52 which controls the sample andhold circuit 43. Thus the sampleand hold circuit 43 will be in the hold mode by the time analog to digital conversion beings. A conversion-started signal,

6 62 which provide output triggers of the properlevel-t'o the radar distribution system. For two-dimensional display units, channel} provides a video signal and master trigger. For threedimensional display units,.channels 1 and 2 each pro- ,vide a video signal, four trigger signals (as applicable),

and an elevation analog signal. 4

' The elevation analog signal for three-dimensional displays isI recons'tructed by a digital-to-analog con-' verter 63 which is controlled by a digital-to-analog con- I trol gatingcircuit 64. Positive and negative outputs, 65

and 66-respectively,'of the trigger detector 56 and an early trigger signal 67 are gated in the controlgating circuit 64 to signal a storage register 68 to store the digital elevation code representing the elevation for each radarsweep. Thereadout of the storage register feedsthe analog-to-digital converter 63, which provides an analog elevation output signal 69.

The most important function of the data channel is to process bearing angles. Bearing angle information en- I ters the system in the form of sine and cosine functions,

or thesystem. itself generates the sine .and cosine functions directly from the bearing angle signal. Generating both. sine and cosine equivalents is done to maintainangle accuracy. If a single, absolute value for the angle resulting from the action of the start signal 51, initiates a a clocksignal within the sequencer46 to generate the digital signal'contained in .the storage register 47.. Isolation amplifier 44 also provides a reset signal 54 to storage register 47 before revised elevation data is to be sent in. The serial output 47av of storage register 47 is then applied to the summing amplifier 42 and is subsequentlyrecorded on magnetic recorder 6. During playback of the recorder 6 the composite video signals. from track-s2, 4, and'.5 arefed three identical video reproduction channels1,2 and 3 (FIG;

5b). Videoreproduce channel 1 contains a video detector 55, a trigger detector 56, and an elevation angle de tector 57. These detectors separate video; trigger, and

elevation signals respectively from the composite video signal 13. The output 58of the video detector '55 ,is' a demodulated video signal that simulates the original video signal recordedfrom the search radar system. pulse signal 59 from ya blanking pulse gate and shaping circuit 70 controls a blanking circuit in an output amplifier 60 of the video channelrThe blanking signal infsures that no trigger signals are left in the yideoLTrigger signals detected from the composite video signal are processed bya gating and shapingcircuit 61 toreconstruct theproper timing relationships among the triggers and to standardize the output trigger. widths.

.Master and'early trigger signals from the fgating' circuits provide timing control for generation of the blanking signal applied to the video output amplifier 60. The outputs of the gatingand shaping circuit 61 are four separate trigger signals applied to trigger driver circuit were used, it might be subject to degeneration or even mismatch between radar and display systems. The sine and cosine functions, however, maintain aspecific relationship both to each other and to the angle from which theyare derived. For example, a 30 bearing might be equal to 10 volts-or 2'volts or l7volts (depending one given system), but a sine function of 0.5 and a cosine function of 0.866 always represent 30.

With respect now to FIG. 6, in processing sine and cosine information the signs of the values are extremely important since they specify the quadrant in which the anglev is locatedfFor example, a plus sine value and minus cosine value for. an angle place the angle in the second quadrant. The sine and cosine values define the anglewithin the quadrant.

Referring now to FIGS. 7a through 7d, bearing data the system in analog form as either synchro signals 19 or scalar signals 20. The analog converter 22 takes this information, generates sin e and cosine analog equivalents, and then changes both the sine and cosine analogs into-binary numbersfWhere the radar develops digital bearing angle datafthis data will be in a different digital fdr iiiit froirn'that which is required within the subjectinvention. The digital converter 23, therefore,

must reformat this data into a usable form. The result ing binary numbers are temporarily stored until the proper address word occurs, thenthey are fed out to a master controller 24a (FIG. 7c). More specifically, the OR gate 24, format generator26, and program control 'formatsthe data 27 to be-recorded on track 30f the magnetic recorder6. The formatter 26 takes all the parallel bits of words and'puts them into a serial form placed atv the proper address. It then inputs this serial train of words onto the magnetic recorder 6.

Referring again to FIG. 1, there are four main units involved in the data record channel; the formatter 26,

the OR gate 24, the analog/digital converter 22, and the digital converter 23. The analog converter receives either synchro 19 or scalar 20 analog voltages and produces a binary equivalent. The input signals are first converted into a common analog voltage range; then the analogs are multiplexed, and the multiplex signal is serially converted into parallel binary numbers. The

- analog converter record circuitry 22 has three sine/cosine synchro converters 75, 76, and 77 (FIG. 7a) that acceptfive-wire synchro analog inputs and produce sine and cosine equivalent analogs. Each con- .verter produces analog voltages proportional to the sine and cosine of that function. For example, assume that the bearing angle is 120. The sine of this angle is +0.866, and the cosine is 0.500. The output of each converter is therefore +8.66 volts sine and .00 volts cosine. The analog converter record'circuitry 22 also has two scalar attenuators 78 and 79 that attenuate X and Y scalar analog inputs to approximately half their ,input magnitudes. It also provides for two interface cards 80 and 81 for processing auxiliary inputs. An analog-control'circuit 74 (FIG. 7b) determines the multiplex sequencing of multiplexer 73 by generating word gates associated with each input. As stated previously, the subject invention can accommodate up to three radars; the three synchro signals and the three digital signals must share the three word-pair gates. Thus, if a digital signal is being used, only two of the synchro signals may be used.

The analog converter 22. must process up to l2 signals: sine-and cosine for three synchro radar inputs, sine and cosine for two scalar radar inputs, and analog data for two auxiliary inputs. Rather than provide 12 separate circuits to individually convert the 12 sources of data to a digital code, the system instead multiplexes the twelve signals and then converts them, serially, one at a time. One multiplexer 71 (FIG. 7a) accepts the cosine inputs and the other multiplexer 73 accepts the sine inputs, the auxiliary data inputs and the composite signal out of multiplexer 71 as processed by a sample and hold circuit 72. A sample and hold circuit 82 (FIG. 7b) samples a portion of each multiplexed analog signal 83 and holds it at that level for the duration of a word. This presents a steady level to an analog-to-digital converter (ADC) 84. The ADC consists ofla comparator 85, a sequencer 86, and a storage register 87. The comparator 85 compares the input analog level signal88 with the summed level signal 89 caused by the feedback from the output of the ADC. If the two levels are not the same, an output signal 90is applied to the sequencer 86. Based on the start pulse 91 from the analog control, the sequencer beings a binary count and places the count into the storage register 87. At each count, the count is fed back via feedback loop 92 to be compared with the analog input level. At some point the two levels balance, and the number stored in the register 87 represents the analog value in an equivalent binary number. Because the ADC 84 uses a binary count, a code converter 93 takes the ADC output signal 94 and converts it to a parallel number that is compatible with the system binary code.

The digital converter 23 via a receiver 95 (FIG. 7a) receives positive input pulse trains representing the sine (X data) and cosine (Y data) of the radar bearing angle, and it generates from each a l2-bit binary equivalent. Three identical channels 96, 97, and 98 (FIG. 7a) one for each of the three radars comprise the digital converter circuit 23. The converter 23 synchronizes its data with the radar by taking the endof-sweep 34 and range mark 99 pulses and generating a simulated master trigger signal 100 in a trigger generator 101. Data is stored in X and Y storage registers 102 and 103, respectively, (FIG. 7b) for readout to the formatter 26 at the appropriate word gate.

The input from the radar is a pulse train representing the sine of the bearing angle and a pulse train representing cosine. The number of pulses in each train corresponds to the value of the sine and cosine function, and the pulse spacing corresponds to range. Thus, for example, since the sine of 30 is 0.500 and the cosine is 0.866, the X data (sine) might be 500 pulses and the Y data (cosine) might be 866 pulses. This would define the bearing of the radar, but it would not define the range of the radar. If the pulses are at the maximum pulse repetition rate, the radar range is therefore maximum; if the pulse repetition rate is half receiver which consists essentially of operational amplifiers that limit and shape the input pulse thereby providing a constant amplitude output. There are four key elements to the digital converter 23. One is the trigger generator 101 that starts the sequence. The second is a gate generator 108 that permits X and Y pulses to pass during the gate period. The third element is comprised of X and Y counters 109 and 110, respectively, that count the X and Y pulses. The fourth element is comprised of the storage registers 1 02 and 103 that store the count and thus allow the data to be timing synchronized; The trigger generator 101 receives the e'nd-of-sweep (EOS) trigger 34 and the range marks 99 from the radar. The EOS trigger 34 sets a flip-'flop within the trigger generator and the subsequent range mark signal 99,, which coincides with range zero and therefore is equal to a master trigger, resets the flipflop. The reset, or trailing edge, of the flip-flop fires a single-shot output to produce the simulated master trigger output 100. This trigger signal sets a latched-gate flip-flop circuit 111 which consists of latched NAND gates. Output signal 112 of flip-flop circuit I] lean be considered the on gate that regulates clock 113 in a gating circuit 115. There are two clock rates. The fast rate in the preferred embodiment is 16 times that of the slow rate. The fastrate corresponds to one particular radar system while the slow rate corresponds to another radar type. The setting of a select switch 114 causes gating circuit 115 to gate through either the fast or the slow clock during the on period of output signal 112. A gated clock output signal 116 toggles a control counter 117, causing it to count up to maximum. At the end of the count, the control counter 117 emits an end-of-count pulse 118 that clears the latched-gate flip-flop 111 causing the output gating signal 112 to go off.

During the on" period of the output gating signal 112, the receiver 95 conditions and passes the X and Y data 104 and 105, respectively, as well as the signs of X and Y data, 106 and 107, respectively. The data pulses are gated through to the X and Y counters 109 and 1 10, respectively, which merely count the number of X and Y pulses. The X and Y counts 119 and 120 respectively, in parallel form, are applied to the X and Y storage registers 102 and 103, respectively, (FIG. 7b) along with the signs of X and Y data, 121 and 122 respectively. At the end of the gate of output gating signal 112, X and Y pulses from the receiver are inhibited from the X and Y counters by the closing of data gates 123 and 124. At this point, the binary counts from the X and Y counters 109 and 110 respectively hold the equivalent binary numbers of the pulse train. As the gate of output gating signal 112 goes off, it causes a delay circuit 125 to emit a delay pulse signal 126. This delayed pulse signal 126 is the reset to the storage registers 102 and 103, and it clears them to receive the data from the X and Y counters 109 and 110 respectively. A second delayed pulse 127 produced by delay circuit 128 sets the registers, permitting the parallel counts from the X and Y counters to enter the registers. Then, a third delay pulse 129 produced by a delay circuit 130 resets the control counter 117 and both data counters by way of the reset direct (R inputs 131, 132, and 133. At this point, the storage registers 102 and 103 hold the binary equivalent of the X and Y functions of the bearing angle. If that particular channel is being used, word gates for radars l 2, and 3 are routed to the three channels at 134, 135 and 136 respectively. These are the same word gates used in the analog converter 22, so obviously only three types of radar signals out of the total six possibilities (three synchro and three digital) can be used at any one time. The word gates via gating circuit 137 read out the X data during the particular even word, and read out the Y data during the particular odd word. The data, still in parallel form, is fed out through a driver circuit 138, along with a strobe (STB) pulse 139. The STB pulse is subsequently used to strobe the data into the formatter 26. If this pulse is not present, data for that frame is lost. To produce true data, the STB pulse 139 results from gating in gating circuit 137a the word gates outputs 140 and 141 with the end of the count signal 118 from the control counter 117 (FIG. 7a). Thus, if the output gating signal 112 is in the process of changing when the word gate appears causing a possibility of reading out to the storage registers 102 and 103 while it is reset the STB pulse 139 is inhibited. The X and Y data 143 and 144 respectively, plus the STB pulse 139, are fed to the common driver circuit 138 from all three channels. The output 145 of driver circuit 138 consists of parallel binary numbers representing sine and cosine for each channel.

A coded time converter circuit 146 (FIG. 70) accepts lRlG B coded time. The coded time signal 147 contains several binary-coded numbers denoting the time of day and the day of the year. This signal may be either positive or negative pulse logic, or it may be carrier-modulated. An interface circuit 148 accepts any of these signals and generates a positive logic, pulse .train output signal 149. The pulse train feeds a shift register 150, and each stage of the shift register becomes a parallel data output to a storage register 151. The control circuit 152 senses the pulse train 149 to determine the start of the frame; fromthis it generates a clock signal 153 for shifting the data into the shift register 150, and it generates set and reset pulses 154 and 155, respectively, to the storage register 151. Since all the desired data occurs during the first 41 bits of the frame, the control circuit 152 allows the shift register to shift in the first 41 pulses. At this point, the first stage of the shift register holds bit 41, the second holds bit 40, etc., until the shift register 150 clears the storage register 151, and then sets in the 41 parallel bits of data. The parallel data is then sent to a time and ID (identification) transfer gate circuit 156.

A time and ID control sequencer 157 generates the subframe gates at 158 and 159 that carry all the slow changing data. The subframe gate consists of certain address words, eg time that does not change as fast as the normal frame rate. Consequently, a subframe will equal several normal frames and will occur at only a fraction of the normal frame rate. Some of these subframe gates 158 are sent to the time and ID transfer gate circuit 156 to gate through the coded time data. The other subframe gates 159 go to switchregister 160 to gate out identification data 161. The sequencer-.157 also generates at 162 the STB pulses for the subframe words and sends them to a parallel data OR gate 24.

The control circuit 163 includes a clock and control counter 164 and a word and marking gating circuit 165. The clock and control counter 164 generates various counts from a basic crystal oscillator frequency. The word and marking gating circuit 165 combines these counts in various ways to produce a frame marker 166 indicating the start of each frame, word markers 167 indicating the start of each word, word gates 168 for the start of various other data, and other special markers 169 (triggers). The frame and work markers 166 and 167 respectively go to the formatter 26 for insertion into the 96-word frame format, while the word gates 168 are distributed to the specific circuits dealing with the data that goes into those particular word addresses.

The final data that is processed through the time and ID transfer gate circuit 156 is a scan count signal 170. A zero crossover detector circuit 171 senses the signs of the sine and cosine functions for each of the three recorded radars. Since there is only one point (zero bearing) where the cosine is positive at the instant that the sine goes positive, this circuit senses this point and sends a trigger 172 to a scan counter 173.

A self-test control circuit 174 generates a word pair gate signal 175 that is used to test the operation of the circuit. The self-test control circuit 174 sends an inhibit signal 176 to block passage of the normal data while self-test data is routed to the formatter 26 instead. Selftest data consists of binary-coded words that, like the other data coming out of the OR gate 24, is in parallel. At this point, all data exists as parallel bits occurring during their assigned word addresses. All the data is made into a composite parallel signal by the parallel data OR gate 24. Parallel data is placed into even and odd shift registers 177 and 178, respectively, (FIG. 7d) at each bit stage through the set direct (S inputs 179 and 180 respectively. The S inputs are produced by even gate circuit 181 and odd gate circuit 182, respectively. In either case, the data is shifted through each shift register by clock signals 183 and 184 which are produced from gating circuits 185 and 186, respectively. Half of the formatter 26 handles even words, while the other half handles odd words. This is done so that one half can be loading while the other half is dumping. All the data is gated to the even or odd portion of the circuit by even and odd word gates.

Serial data from outputs 187 and 188 of even and odd shift register circuits 177 and 178 are combined in gating circuit 189 with the frame and word markers 166 and 167, respectively, from the word and marking gating circuit 165 (FIG. 7b) and are sent into the format converter 190. The format converter puts the data into a modified Manchester code format and applies it to a bipolar driver 191. The bipolar driver provides the power to drive the signal, passing it to the magnetic recorder 6 (FIG. 1).

The data channel reproduce circuitry of FIGS. 8a through 8d, like its counterpart in the video channels, reverses the record circuitry procedures. The decoder 28 (FIG. 1) separates the various words and places them in parallel form, except for that data that must go out in serial form. The analog converter 29 (FIG. 1) then changes the parallel digital data into an analog equivalent which is fed out as a scalar voltage, and said data is also applied to a servo generator 200 (FIG. 8d). The servo generator changes the simple analog voltage into a synchro analog. The digital converter 30 takes the parallel binary information and generates a pulse train type of digital signal that is identical to the type of signal applied to the record portion of the digital converter. Time and identification information is displayed as is the self-test data.

Referring now with greater specificity to FIGS. 8a through 8d, there is shown the record and reproduce modes for the data channel. There are five main units involved: a self-test circuit 271, the decoder 28, a trig converter 284, the analog converter 29 and its associated servo generator 200, and the digital converter 30 and an associated digital l9 converter 238 (FIG. 8d). In general the decoding circuit receives the serial data from the magnetic recorder, extracts synchronizing pulses for words and frame, generates a clock at the bit rate, provides word gates and converts the data into parallel form. The format decoder 201 (FIG. 8a) receives the serial data 27 from the magnetic recorder 6. From the serial data it generates a clock signal 202 containing 14 pulses; one for each of 12 data bits, one for the sign bit, and one for the parity bit. It also produces a sync signal 203 at the word rate, and it provides complemented serial data 204. A sync control circuit 205 receives the sync signal and the serial data. By gating the sync pulses with the serial data, it extracts the frame marker 207 with which to synchronize a control counter 206. It also provides a word/frame marker pulse 208 for resetting a shift register 209 at the end of each word. In addition, the sync control circuit 205 guards against transmitting false marker pulses (such as noise) and, under certain circumstances, transmits a simulated marker pulse should the original be lost in a magnetic tape dropout. By doing this, it allows the rest of the decoding circuit to continue effective operation.

The control counter 206 provides selected counts. It counts the word/frame marker pulses and resets with the frame sync pulse, providing a final count to the sync control circuit 205 for comparison with the frame sync. A sensor-data decoder 210 clocks the serial data into the shift register 209, and it provides a strobe pulse that occurs after all data for each word is in the shift register. It also takes the drop sync and drop out signals 211 and 212 respectively from the sync control circuit and applies them to lamp circuits 213 and 214. When the two lamps the even 213 and odd 214 lamps are on, they signify that the system is searching for a frame marker and that more than one word marker has not been detected.

The analog converter reproduce circuitry 29 (FIGS. 1 and has three channels for processing three synchro sine and cosine analog drive signals. Two of these three channels can also process scalar sine and cosine analog signals. Parallel data is applied to a code converter 215. Essentially, the code converter reverses the process carried out by the code converter in the record circuit, wherein the data was complemented before it was converted into a binary number. Here, the data is complemented before it is converted into an analog equivalent of the binary number. The data is strobed into scalar storage registers 216 and synchro storage registers 217 by strobe pulse output 218 which is gated by the proper word gate signal 219. The stored binary data is applied to digital-to-analog converters (DACs) 220 through 223, which produce DC analog voltages corresponding to the sine and cosine of the bearing angle. For scalar analogs, amplifiers 224 and 225 boost the voltage to provide the proper excursion for driving the scalar display equipment. For synchro analogs, the voltages must first be converted into synchro outputs, which task is performed by the servo generator unit 200 (FIG. 8d In the servo generator, the sine and cosine voltages are each modulated in modulator 226 into a square wave signal swinging equally about zero or reference. The two signals are resolved in resolver 227 to provide an error signal 229 for a detector 228. The detector 228 integrates the error signal 229 and applies it to a motor amplifier 230. The amplifier provides the drive signal, via a motortachometer protector 231, for driving a motor 232. The motor-tachometer protector 231 senses tachometer 233 overspeed and overload conditions and interrupts the drive signal in the presence of such signals. The motor 232 drives the tachometer 233 and a synchro transmitter 234, and it attempts to null the resolver 227. With a dynamic input (signifying a revolving antenna), some amount of lag in the servo loop between the input and the resolver mechanical nulling results in the error signal 229 being constant to smoothly drive the motor and synchro transmitter.

The digital converter 30 (FIG. 1) generates digital pulse trains which represent the sine and cosine functions of the bearing angle. A clock generator 235 (FIG. 80) receives at input 236 the basic system clock signal 237, generated in the digital 0 circuit 238 (FIG. 8d)

(which will be discussed in detail hereinafter), and

passes a proper clock signal 239 (FIG. 8c). The clock signal 239 is counted by a 17 bit counter 240, and then applied to AX rate multiplier 241 and a AY rate multiplier 242 along with X and Y binary words 243 and 244, respectively, from input storage registers 245. The rate multipliers 241 and 242 combine counts according to the magnitude of the binary number of the X or Y 

1. A radar data recording and reproducing system for recording radar data received from a plurality of tracking radars and subsequently replaying said radar data into a display system, said radar data including video signals, trigger synchronizing pulses, elevation angle signals, radar bearing information and time and auxiliary data, comprising: means for combining said video signals, trigger synchronizing pulses, and elevation angle signals into a composite video signal; means for converting said radar bearing and time and auxiliary information signals into a serially multiplexed digital signal; recording means adapted to severally record said composite video signal and said serially multiplexed digital signal simultaneously; first converting means operably connected to said recording means for reconverting said composite video signal into said video signals, trigger synchronizing pulses, and elevation angle signals; and second reconverting means operably connected to said recording means for reconverting said serially multiplexed digital signal into said radar bearing and time and auxiliary information signals.
 2. The radar data recording and reproducing system as specified in claim 1 wherein said combining means comprises: means for conditioning said video signals, said trigger synchronizing pulses and said elevation angle signals into signals compatible with said recording means and said first reconverting means; and means for summing said conditIoned signals producing thereby said composite video signal.
 3. The radar data recording and reproducing system as defined in claim 2 wherein said conditioning means comprises: means for converting said elevation angle signal into an output digital signal; means for encoding said trigger synchronizing pulses; and means for modulating said video signal.
 4. The radar data recording and reproducing system as recited in claim 3 wherein said first reconverting means comprises: means for separating said conditioned video, trigger and elevation signals from said composite video and including; means for detecting said modulated video signal; means for detecting said trigger synchronizing pulses; means for reconstructing the original timing relationship among said trigger synchronizing pulses; and means for converting said digital elevation signal into the originally received analog elevation signal.
 5. The radar data recording and reproducing system as recited in claim 4 wherein said radar bearing signal may be present, at any given time, in the form of either an analog signal or a digital pulse train and wherein said serially, multiplexed digital system converting means comprises: means rendered effective when said radar bearing signal is in the form of a scalar or synchro analog signal for generating an analog signal representing the sine and cosine of radar bearing; means for converting said analog sine and cosine signal into a corresponding parallel digital signal; means rendered effective when said radar bearing signal is in the form of a digital pulse train for converting said digital pulse train into a corresponding parallel digital signal; means responsive to said trigger synchronizing pulses for converting said trigger synchronizing pulses into a corresponding parallel digital signal according to a predetermined timing format; serial formatting means capable of transforming an input parallel digital signal into a serially formatted digital signal according to a predetermined timing format; and OR gating means connecting the input of said serial formatting means selectively to the outputs of said analog sine and cosine converting means and said digital pulse train converting means.
 6. The radar data recording and reproducing system as recited in claim 5 wherein said second reconverting means comprises: decoding means connected to the output of said recording means for converting said serially multiplexed digital signal into radar bearing information signals, trigger information signals and time information signals, all of said signals being in parallel binary form; analog converting means for converting said parallel digital radar bearing information into scalar and synchro analog signals, means for receiving said digital parallel binary information for converting said information into digital pulse trains representing sine and cosine functions of said radar bearing signal; and means for recovering said timing information.
 7. The radar data recording and reproducing system as defined in claim 6 wherein said elevation angle converting means further comprises: means for sampling said analog elevation angle signal at each radar sweep, said sampling being controlled by said trigger synchronizing pulses; and means responsive to said output digital signal and to said sampled analog signal for producing an error signal therefrom, said error signal serving to periodically revise said output digital signal.
 8. The radar data recording and reproducing system as specified in claim 6 and further comprising self-test circuit means operably connected to the output of said decoding means for instantaneously determining the angular value of said radar bearing angle.
 9. The radar data recording and reproducing system as recited in claim 5 wherein said means for generating said sine and cosine equivalents of said scalar or synchro analog signal comprises: sine/cosine converter means for producing analog voltages proportional to the sine and cosine of said synchro or scalar analog signal input; first analog multiplexing means connected so as to receive the cosine equivalent outputs of said sine/cosine converter means; and second analog multiplexing means connected so as to receive the sine equivalent outputs of said sine/cosine converter means and the output of said first analog multiplexing means.
 10. The radar data recording and reproducing system as specified in claim 9 wherein said parallel digital converting means comprises: sample and hold circuit means for sampling a portion of said output of said second analog multiplexing means, said sample and hold circuit means holding the analog voltage level of said output signal of said second analog multiplexing means thereby presenting a constant voltage level for the duration of the multiplexed analog word; and first converting means for converting said multiplexed analog output of said sample and hold circuit means into an equivalent binary number and including; comparator circuit means operably connected to said output of said sample and hold circuit means for comparing the output of said first converting means with said sample and hold circuit output signal; control circuit means wherein said first converting means will initiate said digital conversion as long as said output level of said sample and hold circuit means differs from the output level of said first converting means, and second converting means for converting the binary output of said first converting means into a parallel binary signal.
 11. The radar data recording and reproducing system recited in claim 10 wherein said digital pulse train is comprised of a pulse train representing the sine of said bearing angle, and a pulse train representing the cosine of said bearing angle wherein the number of pulses in each of said digital pulse trains represents the specific sine and cosine numerical value and further wherein said means for converting said digital pulse train comprises: means for counting the number of pulses in each of said sine and cosine pulse trains, said counting means producing thereby a controlled, parallel binary signal output equivalent to said pulse number count; control circuit means for controlling the readout of said counting means, said control circuit means being controlled by said trigger synchronizing pulses; means for converting said controlled, parallel, binary signal output of said counting means into a digital, parallel signal; and timing means for strobing the output of said converting means into said formatting means, said strobing occuring in proper timing relationship with said trigger synchronizing pulses.
 12. The radar data recording and reproducing system as specified in claim 11 wherein said analog converting means comprises: digital-to-analog converting means receiving said digital parallel signal and converting said signal into scalar analog voltages corresponding to the sine and cosine of said bearing angle, said conversion occurring according to a predetermined timing format; and means for converting said digital parallel signal output into synchro analog signals.
 13. The radar data recording and reproducing system as defined in claim 12 wherein said synchro analog voltage converter comprises: means for modulating said sine and cosine signals; said sine and cosine signals having an error therebetween; means for producing a motor drive signal from said error signal; motor means responding to said motor drive signal; and synchro transmitting means operably connected to said motor means for transmitting said synchro signal.
 14. The radar data recording and reproducing system as recited in claim 13 wherein said digital converting means comprises: means for determining from the pulses in said digital pulse train the digital value of said radar bearing signal, Said determination being performed according to a predetermined timing format; and means for converting said determined digital value, said value representing the trigonometric value of said radar bearing data, into angular values of said radar bearing data.
 15. A method of radar data recording and reproducing for recording radar data received from a plurality of tracking radars and subsequently replaying said radar data into a display system, said radar data including video signals, trigger synchronizing pulses, elevation angle signals, and radar bearing information, comprising the steps of: combining said video signals trigger synchronizing pulses, and elevation angle signals into a composite video signal; converting said radar bearing information into a serially multiplexed digital signal; recording said composite video signal and said serially multiplexed digital signal; reconverting said composite video signal into said video signal, trigger synchronizing pulses and elevation angle signals; and reconverting said serially multiplexed digital signal into said radar bearing information. 